This invention relates to a method and apparatus for correcting tracking errors in a transducer which scans successive, parallel tracks of a record medium and, more particularly, to such a method and apparatus wherein the position of the transducer relative to the track being scanned can be adjusted when a tracking error condition is sensed.
Signal recording and/or reproducing apparatus are known wherein the rotary head assembly scans successive parallel tracks on a record medium so as to record signal information by scanning the record medium with the rotary head or heads. The record medium generally used in such apparatus is magnetic tape, magnetic sheets, magnetic discs and various other types of media. In addition to rotating the head or heads across the record medium, the medium also is moved. One particular use of such apparatus is to record video signal information on, for example, magnetic tape, wherein parallel slant tracks are recorded in skewed relation to the longitudinal axis of the tape. In addition to video signal information, such apparatus is capable of recording other types of analog signals or, if desired, digital signals representing various types of information. In the interest of simplification, the following explanation and description refers to video signal recorders which use magnetic tape, such as the video tape recorder (VTR). However, it should be understood that this explanation and description also is applicable to different types of recording apparatus (such as other types of analog or digital recorders) which use different media.
A typical VTR includes one, and preferably two, record/playback heads mounted on a suitable rotary assembly so as to rotatably scan a magnetic tape which is helically wrapped about at least a portion of a guide drum. During recording, a tracking servo system synchronizes the movement of the tape to the rotary movement of the heads, and control signals which can be used for this type of synchronism during a reproducing operation are recorded on the tape. Hence, during reproduction, this same servo control system is used to synchronize the movement of the tape to the rotation of the heads. Consequently, a generally accurate video picture can be displayed in response to the reproduced video signals. That is, this servo control system is operative to control the relative movement between the rotary heads and the tape such that each head scans substantially the same track during reproduction as was scanned during recording.
However, even with this servo control system, there are instances wherein the path traversed by the heads during reproduction does not coincide satisfactorily with the recorded record track. This is particularly true when the video signals are recorded by one VTR and are reproduced from the tape by a different VTR. If the orbits of the magnetic heads in these different VTR's are not equal to each other, the servo control system may not be effective to bring the heads into coincidence with the recorded tracks during reproduction. Other factors also may be present which prevent successful operation of the servo control system. Consequently, the scanning magnetic heads may exhibit tracking errors during reproduction.
The tracking errors mentioned above may not be particularly noticeable or objectionable for VTR apparatus wherein parallel tracks are recorded with guard bands separating adjacent tracks or when the magnetic tape is transported at a sufficiently higher speed. However, the problems caused by these tracking errors during signal reproduction may not be accceptable if the guard bands between adjacent tracks are reduced and if the speed at which the magnetic tape is transported is reduced. The desirable effect of eliminating the guard bands, and thus increasing the recording density (tracks per inch), and of reducing the transport speed of the magnetic tape is to increase the amount of video signal information which can be recorded on a magnetic tape of given lengths. This, in turn, increases the recording capacity (generally expressed as a measure of time) of the VTR without requiring a concommitant increase in the supply or length of recording tape. In particular, for these so-called "longer-playing" VTR's, tracking errors may reduce the signal-to-noise ratio and may otherwise deleteriously affect the reproducing characteristics.